1. Field of the Invention
The present invention relates to methods and apparatus for mixing a small, steadily metered rate of bulk materials without wastage into a liquid stream, and is particularly useful for preparing an innocular solution for treating animal feed, seeds or the like.
2. Description of the Prior Art
In recent years, increased interest has been directed toward pelleted animal feeds which are treated with an innoculant of one type or another. Once ingested, the innoculant or bacteria live within the intestinal tract of the animal and produce lactic acid which prevents growth of harmful types of microorganisms that might otherwise cause digestive trouble.
It is possible to mix the innoculants with the various materials comprising the feed before pellitization. However, heat used during the pelletting process may seriously harm or kill the bacteria which normally is relatively expensive. Moreover, it is difficult for the average feedlot owner to test the pellets after formation to ensure that the bacteria are viable.
As a result, it has become common practice to mix innoculants with the feed after the pellet is formed. Typically, a quantity of bacterial powder is measured by hand and added to a tank containing a specific, measured quantity of oil. A stirrer within the tank is provided in an attempt to maintain the bacterial powder in suspension, and the tank is then pressurized to direct the mixture through a spray nozzle and onto previously formed feed pellets.
The use of oil such as mineral oil as a carrier for the innoculants is advantageous because the oil adheres to the pellets and essentially fixes the bacteria in place until ingested. Moreover, oil based carriers are superior to water based carriers in that the bacteria become activated once mixed with water and thus survive only a short time unless immediately fed to the animals.
Unfortunately, many problems have been associated with the use of batch type, pressurized mixing tanks for innoculation of feed pellets. First, the size of the batch must be estimated in advance so that a sufficient amount of mixture is available for treating the expected quantity of feed. Often, an amount of the oil and innoculant mixture in excess of the estimated needs is prepared so that treatment for all of the feed is somewhat assured. However, such practice normally leads to wastage of the relatively expensive innoculant material which cannot be saved in viable condition in the tank from one day to another.
On the other hand, it is particularly undesirable to underestimate the amount of oil and bacteria mixture for treating a quantity of feed due to the time and labor needed to precisely measure additional quantities of oil and innoculant powder for a second batch. Moreover, such practice increases the likelihood that either the oil or powder will be incorrectly measured.
Furthermore, batch type, pressurized tank mixing apparatus must be thoroughly cleaned after each use to prevent the growth of algae and other undesirable organisms. In essence, the interior walls of the tank, the stirrer and other components must be extensively scrubbed to remove all residue of the mixture.
Another problem associated with the mixing of oil and innoculants in a batch type tank is the tendency of the innoculants to settle. Use of a stirrer within the tank alleviates this problem somewhat, but it is difficult to attain a truly homogeneous mixture within all regions of the tank. As a result, portions of the mixture sprayed on the certain feed pellets may have a higher concentration of bacteria than other portions of the mixture applied to other pellets.
In some instances, it is desirable to mix three or four different chemicals or types of bacteria in an oil solution. In batch type mixing apparatus, however, the chemicals may react with each other if residence times in the tank exceed a certain value.